1. Field of the Invention
The invention is directed to a process for informing a central bureau about the path traveled by a vehicle in a traffic network, to a terminal unit and to a central bureau.
2. Description of the Related Art
The detection of the path of a vehicle is suitable for detecting erroneous routes in interactive navigation and for obtaining geographic traffic information that can be referenced; This traffic information can be used by a central bureau for correlating traffic data such as vehicle speeds, travel times, etc. with locations on the path of the vehicle, namely with locations in a digital map of the traffic network in the central bureau, wherein traffic status reports, traffic forecasts and optimum navigation assistance can be generated in the central bureau based on traffic data from a plurality of vehicles for transmission to a vehicle. Location data relating to the path of the vehicle through a traffic network can be transmitted, especially via mobile radio, from the terminal unit in the vehicle to a central bureau. The available transmission capacity of the communications channel is limited; in particular, telecommunications costs are increased by the transmitted quantity of information.
EP-A-0 731 400 discloses a process for informing a central bureau about a path traveled by a vehicle in a traffic network, wherein the vehicle location is repeatedly detected by the vehicle with a GPS system and reference points to be transmitted to a central bureau are defined when existing criteria relating to the maximum vertical distance of a detected position to a vector line are met. In this case, reference points are set more frequently when driving along curves than during straight driving due to the fact that a predeterminable maximum vertical distance from a vector line is exceeded more frequently in the first instance.
It is the object of the invention to inform a central bureau about the path traveled by a vehicle in a traffic network with the smallest possible amount of transmitted information which represents the path of the vehicle in the traffic network in the most efficient manner and with the most accurate reconstruction possible.
The invention optimizes the transmitted amount of information about the path of the vehicle. Nevertheless, the path can be reconstructed in a favorable manner because reference points at which information is transmitted are defined at relevant locations along the path of the vehicle. The criteria by which it is determined where reference points are defined at locations along the path of the vehicle through a traffic network are, or can be, predetermined in the terminal unit. These criteria can be modified via radio, especially mobile radio, by a central bureau for a terminal unit. Reference point information concerning the defined reference points is transmitted. This information can contain the last detected location of the terminal unit in particular. Further, it can contain the current driving direction of the terminal unit.
For this purpose, the location can be detected by the terminal unit with a position detection device, particularly with GPS. The location detection of the terminal unit depends on a digital map, etc.
It can be determined from location data detected from at least two locations along the path which are driven through successively which direction the vehicle is driving in between these direction data representing at least two locations. Alternatively or in addition, it is possible to determine the direction of the vehicle with a direction detection device, especially a compass or a digital map in conjunction with means for determining the mileage and/or means for determining the steering wheel angle, etc. Driving data representing the driving direction of the terminal unit at one location or between at least two locations can be transmitted from the terminal unit to the central bureau. In particular, direction data can also be determined as angles relative to the given direction, for example, relative to a cardinal direction, wherein it is useful to determine the cardinal directions in the terminal unit, e.g., by means of a compass and/or position tracking with a digital map. Angular changes within a given unit of time can be detected from the direction data or from angle data representing an angle at least at two locations. Accordingly, a change in direction of the vehicle can be determined. With a suitable selection of the time unit, brief changes in direction, e.g., when passing another vehicle, etc., can be filtered out and only relevant changes in direction, for example, turning onto a road, driving along sharp curves in a road, etc. which are significant for a central bureau are detected and can be used in the terminal unit for defining a reference point.
A storage device (memory) is provided for storing data in the terminal unit wherein a circular storage device is used, it is possible to store the most recent, and therefore particularly relevant, data with small storage capacity.
Further, speed data representing the speed of the vehicle is preferably detected by the terminal unit; when this data is sent to the central bureau, it can be used for preparing traffic status descriptions and accordingly for traffic reports and traffic forecasts in the central bureau.
The reference points can be defined in the terminal unit in different ways. In particular, a reference point can be defined when the vehicle has traveled more than a predetermined or predeterminable minimum distance limit since the last reference point, and when the vehicle angle within a predetermined or predeterminable time unit (which can be set by a central bureau to a terminal unit via mobile radio in particular) changes by more than an angle limit value which is predetermined or can be predetermined (by a central bureau). For this purpose, at least two angles (or directions) of the vehicle at least at two locations are compared in the terminal unit and the resulting difference is compared with an angle limit. When the angle exceeds the angle limit, a reference point can be defined. Accordingly, it is possible in particular to detect relatively sharp curves in a road along a path traveled by a vehicle and changes in direction of a vehicle resulting when turning off of a road which are significant for reconstruction of the path of the vehicle in a central bureau and for correlating the vehicle path with a digital map in a central bureau.
Beyond this or instead of this, a reference point can also be defined when the vehicle advances by more than a predetermined or predeterminable maximum distance limit. For this purpose, the terminal unit preferably detects the advance of the vehicle based on a vehicle distance gauge (mileage counter) and/or location determination at at least two locations and by calculating the difference between these two locations. Therefore, a reference point is defined at least in given limiting intervals along the path. Accordingly, even when the driving direction of the vehicle does not change, reference point information is transmitted from the terminal unit to the central bureau at least in these intervals. Advisable values for the angle limit and for the distance limit are 45xc2x0 and 1000 m, respectively.
Further, the defining of reference points can depend on a stability state that is defined by the extent of current angular changes. For this purpose, the stability of the vehicle can be defined such that the state is unstable when angle changes of the vehicle exceed an angle stability limit (e.g., 10xc2x0) which is advisably less than the angle limit (45xc2x0) and the state is stable below the angle stability limit. The definite of a reference point can be omitted as long as an unstable state exists. However, a reference point can be defined when the unstable state exists along a distance stability limit (e.g., 150 m) which is advisably less than the maximum distance limit. During an unstable state according to a distance stability limit (e.g., 150 m), a reference point is defined in spite of persisting instability (that is, angle changes above the angle stability limit). Accordingly, when a vehicle undergoes changes in angle within a distance exceeding the angle stability limit but below the angle limit, the definition of a reference point is delayed until the distance stability limit is reached. Accordingly, short-term angle changes such as occur when changing lanes, hunting for a parking space, etc. are filtered out and/or definition of a reference point within a curve is prevented.
The criteria for defining a reference point in the terminal unit are preferably variable and can be modified by a central bureau, especially via mobile radio. In this respect, the angle limit, the maximum distance limit, the minimum distance limit and/or the angle stability value, the distance stability limit can be changed in particular. Further, the data to be sent from a terminal unit to the central bureau at a reference point or concerning a reference point can also be changed.
The transmission of data from a terminal unit to a central bureau preferably comprises a transmitted data record containing data concerning a plurality of reference points, especially concerning the most recent reference points that the terminal unit in the vehicle has passed through.
Additional data such as vehicle speed, vehicle speed variants, etc. can also be transmitted at reference points from the terminal unit to the central bureau in addition to location data, particularly at reference points.
The process according to the invention can be realized in a software program in a terminal unit or in a central bureau.